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I have a running systemd unit and I want to follow it's log.

I know I can show unit's log by using:

journalctl -u my_unit.service

But that only prints current logs without following them.

I know I can also follow systemd logs by using:

journalctl -f

But that spams the output by following all known logs, so I have to search for what I'm interested in.

A temporary solution seems to be piping followed logs to grep filtering the output, but that's not very systematic solution:

journalctl -f | grep "what i'm interested in"

Isn't there a command for following logs of certain unit?

What I've tried, but didn't work:

journalctl -uf my_unit.service
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1 Answer 1

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37

I've found out I'm using the arguments in a bad order. Logs can actually be followed for a single unit by using:

journalctl -fu my_unit.service

Other working variations:

journalctl -f -u my_unit.service
journalctl -u my_unit.service -f

From journalctl manual:

-u, --unit=UNIT|PATTERN

    Show messages for the specified systemd unit UNIT (such as a service unit), or for any of the units matched by PATTERN. If a pattern is specified, a list of unit names found in the journal is compared with the specified pattern and all that match are used.  For each unit name, a match is added for messages from the unit ("_SYSTEMD_UNIT=UNIT"), along with additional matches for messages from systemd and messages about coredumps for the specified unit.

    This parameter can be specified multiple times.

-f, --follow

    Show only the most recent journal entries, and continuously print new entries as they are appended to the journal.

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